PROJECT SUMMARY/ABSTRACT Adolescent substance use disorders (SUDs) present a significant public health concern. Adolescents have high rates of relapse following SUD treatment, higher even than adults. Although much is known about risk and resilience pathways for the development of adolescent SUDs, much less is known about predictors and mechanisms of successful versus unsuccessful SUD treatment in adolescents. One mechanism that has shown promise in predicting poor treatment outcomes for adults is high distress intolerance (DI): the inability or perceived inability to withstand distressing emotions. The proposed research focuses on baseline levels of DI, as well as change in DI during and following an existing residential and intensive outpatient treatment program for adolescents. Approximately 134 adolescents will complete a comprehensive assessment of DI, including self-reports, physiological measurements, and DI tasks at baseline, 3 times during treatment, and 3 times during the 6-month follow-up period. Adolescents and parents will also complete assessments of known risk factors for the development and maintenance of SUDs, including adolescent and family substance use history, peer substance use, parental monitoring, social support, trauma symptoms, and internalizing/externalizing problems. During treatment and follow-up, adolescents will report their level of substance craving and substance use relapses. Based on participants' baseline DI and DI change over time, in combination with other measured risk factors, results of the proposed research will be used to predict levels of craving and future relapse. Specifically, results will provide within- and between-subjects profiles of adolescents at risk for a DI-based relapse. Further, because of the multiple assessments within subjects, the results of the proposed research can inform future interventions by demonstrating when a DI-based intervention might be the most needed or beneficial. Finally, in accordance with the key objectives of the AREA R15 program, students will gain invaluable experience in rigorous and intensive research in the areas of addictions, change mechanisms, and recovery. Students will participate in the implementation of research protocols, data analysis, manuscript preparation, and research presentations at conferences, strengthening the students' future career prospects, as well as enhancing the university's research environment.